delta C-13(org) chemostratigraphy of the Permian-Triassic boundary in the Maitai Group, New Zealand: evidence for high-latitudinal methane release

Carbon isotopic studies from marine organic matter of the Permian-Triassic Maitai Group, New Zealand, reveal a significant delta(13)C(org) shift towar d more negative values within the Little Ben Sandstone Formation. These iso topic data chemostratigraphically define the previously debated position of the Permian-Triassic boundary in the Maitai Group. The Permian-Triassic re cord of the Maitai Group is also important because of its high paleolatitud inal setting and the deposition at intermediate depths in the ocean (c. 400 m) within a volcanic arc-related basin. Marine Permian-Triassic strata dep osited at water depths deeper than shelf areas are rare. High latitude Perm ian-Triassic boundary sections document a significantly larger isotopic off set across the boundary compared with lower latitude settings. Carbon isotopic values decrease rapidly by an average of 7 parts per thousa nd from homogeneous values ((x) over bar -25 parts per thousand) in the Tra mway and lower Little Ben Sandstone Formation to highly fluctuating and ver y depleted values ((x) over bar -32 parts per thousand) within the Little B en Sandstone Formation. The lowermost Big Ben and Tramway Formations are co nsidered to be Permian in age, based on their homogeneous and comparably he avier carbon isotopic values and supported by fossil atomo-desmatinid bival ves. Based on the distinct delta(13)C(org) excursion toward negative values and the concurrent onset of strong isotopic fluctuations, the Permian-Tria ssic boundary is placed in the lower half of the Little Ben Sandstone Forma tion. Very depleted delta(13)C values in the Little Ben Sandstone Formation of-38 parts per thousand indicate a contribution from isotopically light methane . A possible methane source is clathrates, released by large submarine slid es or warming-induced melting of permafrost. The Little Ben Sandstone Forma tion has been interpreted as a massive event deposit from a submarine slide (Landis 1980). This hypothesised methane release could have been in part r esponsible for the larger Permian-Triassic isotopic shift in high latitudes compared with low latitudes because large volumes of clathrates are trappe d in continental shelves and high-latitude permafrost.